Process of silver extraction.



UNITED STATES PATENT OFFICE.

FRANCIS J. HOBSON, OF GIIANAJUATO, MEXICO. PROCESS OF SILVER EXTRACTION.

Specification of Letters Patent.

Patented Aug. 7, 1906.

Original application filed July 18,1905, Serial No. 270,300. Divided and this application filed December 20, 1905. Serial No. 292,555.

To all whom it may concern:

Be it known that I, FRANCIS J. HOBSON, a citizen of the United States, now residing at Guanajuato, in the Republic of Mexico, have invented certain new and useful Improvements in Processes of Silver Extraction, of which the following is a specification.

My. present invention consists of an improved process for extracting silver from its ores, and particularly from ores in which the silver'is present in combination with sulfur. Sulfur being present in almost all silver ores, the improved process is of very general application.

Briefly outlined, the process consists of treating the orcs after such preliminary sizing as may be desired with a solution containing a mercurous potassic cyanid. This salt, the characteristics of which are de-. scribed in my previous application, Serial No. 270,300, filed July 18, 1905, of which the present case is a division, has a selective affinity for silver in combination with sulfur. This selective aflinity I have demonstrated experimentally a great many times. The formula of the salt is KHgOy It forms with silver, when in combination with sulfur, a double saltthe cyanid of silver and potassium-which is freely soluble water, and also the sulfid of mercury, which is substantially insoluble in water and passes off with the tailings. The reaction to which I here refer is expressed verbally as follows: Silver sulfid plus mercurous potassic cyanid e uals cyanid of silver and potassium plus suliid of mercury, and in chemical symbols the reaction is expressed thus:

AgS KHgCy KAgCy HgS.

The solvent which I employ in my improved process does not attack gold in any of the forms in which it appears to exist in ore, and although it forms the same salt of silver and potassium in solution as cyanid of potassium when the latter dissolves silver it does not do so in the same way, since potassium cyanid dissolves silver by the well-known Elsners equation, stated verbally as follows: Silver plus cyanid of potassium plus oxygen plus water equals cyanid of potassium and silver plus potassium hydrate or caustic potash. This equation in chemical symbols is stated thus:

2Ag 4K0y o H2O axA c axon.

The same equation applies to the solution of gold, gold replacing silver in it.

ree oxygen in solution is necessary to dissolve silver or gold and form the double salt of potassium and silver or gold with cyanogen.

may produce the mercurous potassic-cyanid in any desired way, since the particular method of its production does not seem to affect the results. I may, for example, add mercurous chlorid (Hg,Cl to a solution of potassium cyanid, (KCy.)

Another method which I may use is to add mercuric chlorid (corrosive sublimate, HgCl to the ordinary mill cyanid solutions containing ferrocyanid of potassium, in which case the reaction may be stated verbally thus: Ferrocyanid of potassium plus mercuric chlorid equals ferrocyanid of mercury plus chlorid of potassium. This reaction may be expressed in chemical symbols as follows:

This is succeeded by the following reaction: Ferrocyanid of mercury plus cyanid of potassium equals ferrocyanid of mercury and potassium plus mercurous potassic cyanid. This reaction. may oe expressed in chemical symbols as follows:

The most suitable strength of the solution is to some extent dependent upon the silver content of the ore and the form in which the metal is present. I have obtained good results with solutions varying from .05 to .50 per cent. The metal may be separated from the solution in any of the approved methods commonly employed in cyanid processes, such as precipitation by zinc dust or shavings or electrolysis.

The solution should be kept alkaline, and this may be effected by the addition of any suitable alkali, such as caustic potash or soda, although in most cases lime will be found to be not only the cheapest, but the best alkali. This application is restricted to that form of my invention in which the mercurous potassic cyanid is formed by the addition of mercuric chlorid to a solution containing ferrocyanid. The other methods of obtaining the solvent, mercurous potassic cyanid, are intended to be broadly covered by my application Serial N 0. 292,554, filed December 20, 1905, which is a division of the parent case, Serial No. 27 0,300, hereinbefore referred to.

Having thus described my invention, What I claim, and Wish to protect by Letters Patent of the United States, is-

1. The process of extracting silver from its ores, which consists of subjecting the ores to the action of a solution of cyanid and ferrocyanid of an alkaline metal, to which has been added mercuric chlorid.

2. The process of extracting silver from its ores, Which consists of subjecting the ores to the action of a solution of ferrocyanid of potassium to which has been added mercuric chlorid.

3. The process of extracting silver from its ores, which consists in subjecting the ores to the action of a solution of the cyanid of an alkaline metal to which has been added ferrocyanid of potash and mercuric chlorid.

4. The rocess of extracting silver from its ores, 'Whic consists of adding to a mill solution containing cyanid and ferrocyanid of potash, a mercuric chlorid.

5. The process of extracting silver from its ores, which consists of subjecting the ores to the action of a solution of cyanid and ferrocyanid -of potash in the presence of a chlorid of mercury and an alkali, and subsequently silver from the solution.

FRANCIS J. HOBSON.

Witnesses WM. 0. YOUNG, H. D. CLEEDE.

precipitating the 

